The invention relates to a process for heating the intake air in internal-combustion engines by means of a flame starting system having an electrically heatable glow plug.
A process of this type is known from German Patent Document DE-PS 33 42 865, corresponding to U.S. Pat. No. 4,624,266. This process concerns a flame starting system in which the air flowing through the intake pipe is preheated in the warm-up phase of the internal-combustion engine to prevent so-called "white smoke". For this purpose, a combustion chamber is provided in the suction pipe of the internal-combustion engine in which a fuel injection nozzle and a glow plug are arranged. For starting the internal-combustion engine at relatively low temperatures, the glow plug is preheated, and after the conclusion of the preheating time, during the starting of the engine, fuel is delivered via a solenoid valve to the fuel injection nozzle and therefore into the combustion chamber of the flame starting system. The fuel ignited in the combustion chamber preheats the intake air flowing past and permits a reliable ignition of the cylinders of the internal-combustion engine at low outside temperatures. A continuous current is fed to the glow plug for the duration of a specific first period of time, until the engine turns over reliably, and, after the conclusion of this first period of time, a pulsed current corresponding to a reduced power is fed to it until the engine has reached a specific operating temperature.
As soon as the engine is ready to start, a safety period is commenced and is terminated by a successful starting operation. If, however, there is no starting operation or if the engine has stopped again within the safety period and after the starting procedure has been carried out, the current to the glow plug is interrupted for safety reasons and to protect the battery after the safety period has elapsed. The flame starting operation is then terminated and the glow plug cools down.
If a renewed starting operation is to be undertaken, the flame starting system must be switched on again and the glow plug preheated again in a manner corresponding to the procedure described above. This renewed preheating operation, however, does not take into account the instantaneous glow plug temperature, which is determined by the cooling period of the glow plug, nor does it take into account the voltage available at the glow plug.
The invention is therefore based on the object of preheating a glow plug, taking into account the instantaneous glow plug temperature and the voltage applied, in such a manner that the temperature required for a repeat start is reached in a simple manner within a narrow tolerance band.
The object is achieved according to certain preferred embodiments of the invention by means of a process for controlling preheating of a glow plug of a flame starting system for heating intake air in an internal combustion engine comprising determining the glow plug temperature based on the cooling time after the glow plug was previously switched off by subdividing the cooling time into discrete time intervals (t.sub.0 -t.sub.1, t.sub.1 -t.sub.2 - - - t.sub.7, t.sub.8) which each have an associated preheating time (t)x value, at least some of said discrete time intervals having different durations based on cooling time versus temperature characteristics of the glow plug, and preheating the glow plug for the associated preheating time (t)x value determined for the respective discrete time interval after switch off of the glow plug.
According to preferred embodiments of the invention, there is provided a process for controlling preheating of a glow plug of a flame starting system for heating intake air in internal combustion engines, comprising determining the glow plug temperature based on the cooling time after the glow plug was previously switched off by subdividing the cooling time into discrete time intervals (t.sub.0 -t.sub.1, t.sub.1 -t.sub.2 - - - t.sub.7, t.sub.8) which each have an associated preheating time (t)x value, preparing a table of preheating times as a function of available voltage and of respective discrete time intervals after switch off of the glow plug, and preheating the glow plug for the associated preheating time from the table.
The invention also contemplates apparatus for carrying out these processes.
After the conclusion of the safety period of a flame starting system and when the engine has not started, the flame starting operation is terminated and the glow plug used in the flame starting system cools down. The instantaneous glow plug temperature is determined by the time measurement, using the cooling curve of the glow plug which has been determined, and the associated preheating time for a repeat start is relayed to the control unit of the flame starting system. If the device is now restarted, each time section of the cooling curve of the glow plug now has its own previously determined value for the preheating time so that the glow plug temperature is always brought to a specifically defined value necessary for the repeat start and located within a permissible range of tolerance.